1. Field of the Invention
The present invention generally relates to a wiring method. More specifically, the present invention relates to a wiring method to be performed on a thin film transistor.
2. Background Information
As is well known, a thin-film transistor (hereinafter also referred to as a TFT) has a configuration including an insulating film, a layer on which a drain electrode and a source electrode are formed, and a layer on which a gate electrode. The drain electrode/source electrode layer and the gate electrode layer are disposed on either side of the insulating film. When manufacturing such a thin-film transistor, the insulating film is preferably made thinner in order to improve productivity. However, since such an insulating film fulfills the role of preventing short-circuiting between the drain electrode/source electrode and the gate electrode, reducing the thickness of the insulating film can sometimes result in insufficient insulation between the drain electrode/source electrode and the gate electrode.
Japanese Patent Application Publication No. 2002-190598 discloses a technique for resolving such problems. Specifically, the thickness of the gate electrode is reduced by adjusting the gradation of exposure using a so-called gray tone exposure technique, such that the portion of the insulating film on the gate electrode is made relatively thick to secure the requisite thickness of the insulating film between the drain electrode/source electrode and the gate electrode.
Recently a method has been proposed wherein a pattern is formed on a substrate using so-called ink jetting, which is a droplet ejection method for ejecting liquid material in a droplet form from a liquid ejection head. In this method, the liquid material (functional liquid) with which the pattern is to be formed is deposited in the shape of the pattern directly onto the substrate, and is then converted into the pattern using a heat treatment or a laser irradiation. This method has merits in that the need for photolithography is eliminated, the process is greatly simplified, and a lesser amount of raw material is required.
It is preferable to reduce the thickness of the insulating film described above in order to improve the productivity even when a TFT is manufactured by applying such a droplet ejection method to form gate wiring or the like, where part of such gate wiring is also used as a gate electrode. In actuality, among techniques for forming gate wiring or the like using droplet ejection, no technique has yet been proposed that would secure the required thickness of the insulating film formed on the gate electrode while reducing the thickness of the gate electrode.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved wiring method that overcomes the problems of the conventional art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.